TROJ_CRYPTESLA.CAL

April 27, 2015
 Analysis by: Ryan Gardo
 ALIASES:

Trojan.CryptoLocker.FKD(Malwarebytes), Trojan.Cryptolocker.N(Symantec), Trojan/Win32.Ransom(AhnLab-V3)

 PLATFORM:

Windows

 OVERALL RISK RATING:
 DAMAGE POTENTIAL:
 DISTRIBUTION POTENTIAL:
 REPORTED INFECTION:
 INFORMATION EXPOSURE:

  • Threat Type: Trojan

  • Destructiveness: No

  • Encrypted:

  • In the wild: Yes

  OVERVIEW

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

It deletes the initially executed copy of itself.

  TECHNICAL DETAILS

File Size:

475,136 bytes

File Type:

, EXE

Initial Samples Received Date:

21 Apr 2015

Arrival Details

This Trojan arrives on a system as a file dropped by other malware or as a file downloaded unknowingly by users when visiting malicious sites.

Installation

This Trojan drops the following files:

  • {randomly selected path}\HELP_RESTORE_FILES.txt
  • %User Profile%\My Documents\RECOVERY.TXT
  • %Application Data%log.html
  • %Application Data%key.dat
  • %Desktop%\HELP_RESTORE_FILES.txt
  • %All Users Profile%\Desktop\HELP_RESTORE_FILES.txt
  • %Desktop%\CryptoLocker.lnk
  • %Desktop%\HeLP_ReSTORe_FILeS.bmp

(Note: %User Profile% is the current user's profile folder, which is usually C:\Documents and Settings\{user name} on Windows 2000, XP, and Server 2003, or C:\Users\{user name} on Windows Vista and 7.. %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %Desktop% is the desktop folder, where it usually is C:\Documents and Settings\{user name}\Desktop in Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\Desktop in Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.. %All Users Profile% is the All Users folder, where it usually is C:\Documents and Settings\All Users on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\ProgramData on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

It drops the following copies of itself into the affected system:

  • %Application Data%\{random filename}.exe

(Note: %Application Data% is the Application Data folder, where it usually is C:\Documents and Settings\{user name}\Application Data on Windows 2000, Windows Server 2003, and Windows XP (32- and 64-bit); C:\Users\{user name}\AppData\Roaming on Windows Vista (32- and 64-bit), Windows 7 (32- and 64-bit), Windows 8 (32- and 64-bit), Windows 8.1 (32- and 64-bit), Windows Server 2008, and Windows Server 2012.)

Autostart Technique

This Trojan adds the following registry entries to enable its automatic execution at every system startup:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\Run
msdedf = "%Application Data%\{random filename}.exe"

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\
Windows\CurrentVersion\Run
msdedf = "%Application Data%\{random filename}.exe"

Other System Modifications

This Trojan adds the following registry keys:

HKEY_CURRENT_USER\Software\Microsoft\
Windows\CurrentVersion\SET

It modifies the following registry entries:

HKLM\SOFTWARE\Microsoft\
Windows\CurrentVersion\policies\
system
EnableLinkedConnections = "1"

HKEY_CURRENT_USER\Control Panel\Desktop
WallpaperStyle = "0"

(Note: The default value data of the said registry entry is {User Defined}.)

HKEY_CURRENT_USER\Control Panel\Desktop
TileWallpaper = "0"

(Note: The default value data of the said registry entry is {User Defined}.)

HKEY_CURRENT_USER\Control Panel\Desktop
Wallpaper = "%Desktop%\HeLP_ReSTORe_FILeS.bmp"

Other Details

This Trojan connects to the following URL(s) to get the affected system's IP address:

  • http://ipinfo.io

It connects to the following possibly malicious URL:

  • http://{BLOCKED}iye577q3p2.{BLOCKED}j3n26.com
  • http://{BLOCKED}ye577q3p2.{BLOCKED}w3n27.com
  • http://{BLOCKED}iye577q3p2.tor2web.{BLOCKED}ie.de
  • http://{BLOCKED}iye577q3p2.tor2web.fi

It renames encrypted files using the following names:

  • {original filename}.ecc

It deletes the initially executed copy of itself